Yuki Sato

Broadband and high-precision two-level system loss measurement using superconducting multi-wave resonators

  1. Cliff Chen,
  2. Shahriar Aghaeimeibodi,
  3. Yuki Sato,
  4. Matthew H. Matheny,
  5. Oskar Painter,
  6. and Jiansong Gao
Two-level systems (TLS) are known to be a dominant source of dissipation and decoherence in superconducting qubits. Superconducting resonators provide a convenient way to study TLS-induced
loss due to easier design and fabrication in comparison to devices that include non-linear elements. However, accurately measuring TLS-induced loss in a resonator in the quantum regime is challenging due to low signal-to-noise ratio (SNR) and the temporal fluctuations of the TLS, leading to uncertainties of 30% or more. To address these limitations, we develop a multi-wave resonator device that extends the resonator length from a standard quarter-wave λ/4 to Nλ/4 where N=37 at 6GHz. This design provides two key advantages: the TLS-induced fluctuations are reduced by a factor of N‾‾√ due to spatial averaging over an increased number of independent TLS, and the measurement SNR for a given intra-resonator energy density improves by a factor of N‾‾√. The multi-wave resonator also has fundamental and harmonic resonances that allow one to study the frequency dependence of TLS-induced loss. In this work we fabricate both multi-wave and quarter-wave coplanar waveguide resonators formed from thin-film aluminum on a silicon substrate, and characterize their TLS properties at both 10mK and 200mK. Our results show that the power-dependent TLS-induced loss measured from both types of resonators agree well, with the multi-wave resonators achieving a five-fold reduction in measurement uncertainty due to TLS fluctuations, down to 5%. The Nλ/4 resonator also provides a measure of the fully unsaturated TLS-induced loss due to the improved measurement SNR at low intra-resonator energy densities. Finally, measurements across seven harmonic resonances of the Nλ/4 resonator between 4GHz – 6.5GHz reveals no frequency dependence in the TLS-induced loss over this range.
arxiv pdf

Observation of topological phenomena in a programmable lattice of 1,800 qubits

  1. Andrew D. King,
  2. Juan Carrasquilla,
  3. Isil Ozfidan,
  4. Jack Raymond,
  5. Evgeny Andriyash,
  6. Andrew Berkley,
  7. Mauricio Reis,
  8. Trevor M. Lanting,
  9. Richard Harris,
  10. Gabriel Poulin-Lamarre,
  11. Anatoly Yu. Smirnov,
  12. Christopher Rich,
  13. Fabio Altomare,
  14. Paul Bunyk,
  15. Jed Whittaker,
  16. Loren Swenson,
  17. Emile Hoskinson,
  18. Yuki Sato,
  19. Mark Volkmann,
  20. Eric Ladizinsky,
  21. Mark Johnson,
  22. Jeremy Hilton,
  23. and Mohammad H. Amin
The celebrated work of Berezinskii, Kosterlitz and Thouless in the 1970s revealed exotic phases of matter governed by topological properties of low-dimensional materials such as thin
films of superfluids and superconductors. Key to this phenomenon is the appearance and interaction of vortices and antivortices in an angular degree of freedom—typified by the classical XY model—due to thermal fluctuations. In the 2D Ising model this angular degree of freedom is absent in the classical case, but with the addition of a transverse field it can emerge from the interplay between frustration and quantum fluctuations. Consequently a Kosterlitz-Thouless (KT) phase transition has been predicted in the quantum system by theory and simulation. Here we demonstrate a large-scale quantum simulation of this phenomenon in a network of 1,800 in situ programmable superconducting flux qubits arranged in a fully-frustrated square-octagonal lattice. Essential to the critical behavior, we observe the emergence of a complex order parameter with continuous rotational symmetry, and the onset of quasi-long-range order as the system approaches a critical temperature. We use a simple but previously undemonstrated approach to statistical estimation with an annealing-based quantum processor, performing Monte Carlo sampling in a chain of reverse quantum annealing protocols. Observations are consistent with classical simulations across a range of Hamiltonian parameters. We anticipate that our approach of using a quantum processor as a programmable magnetic lattice will find widespread use in the simulation and development of exotic materials.
arxiv pdf